This invention relates to compression cycle refrigeration machines, particularly of the type having an air cooled condenser. if the compressor is of the type which will allow refrigerant gas to flow from the evaporator to the condenser during periods when the compressor is not operating, it is possible that the water in the evaporator may become frozen should the condenser be exposed to ambient temperatures below the freeze point. This can happen when the condenser is arranged at a higher elevation than the evaporator. Refrigerant vapor will migrate through or around the compressor to the condenser where it is condensed to a liquid. The liquid refrigerant then may flow by gravitational forces to the evaporator. This liquid refrigerant in the evaporator will then be evaporated causing a cooling effect. Should the refrigeration machine be shut down such that the water in the evaporator is not being circulated, this cooling effect can be sufficient to freeze the water within the tubes of the evaporator. It is to this problem that this instant invention is directed.
Prior hereto, it was the customary practice of the Assignee of this invention to place an expensive solenoid shutoff valve in the liquid line extending from the condenser to the liquid line throttling means. The solenoid was energized simultaneously with the compressor so as to open the liquid line at times when the compressor was operating and to close the liquid line at times when the compressor was not operating. This then had the effect of preventing the natural circulation of refrigerant which could cause freezing of the evaporator tubes under low temperature outdoor ambient conditions. The solenoid valve used for this purpose was of the pilot-operated type which utilized only those pressures immediately upstream and downstream of the valve to power the valve toward the open and closed positions.
The same refrigeration machine also included manual shutoff valves in the liquid line as well as in the gas line extending from the compressor to the condenser. These valves could be manually closed to facilitate servicing the condenser or the compressor and evaporator. These valves are a significant cost in the refrigeration machine. One of the objects of this invention therefore is to reduce such costs by combining one of these manual shutoff valves with the automatic operated valve.
Another objective of this invention is to provide a liquid line valve which is actuated and operated entirely by variations in the refrigerant pressures within the refrigeration machine.
This invention relates to a refrigeration system comprising an evaporator, compressor, condenser, and refrigerant liquid throttling means connected respectively in a closed refrigerant loop; valve means disposed in said loop between the outlet of said condenser and the inlet of said evaporator; valve operator means for operating said valve; and a vent line extending from said valve operator means to the inlet of said compressor; and vent line being disposed to bypass said evaporator.
More specifically this invention relates to a refrigeration system comprising: a closed refrigerant loop including; a shell and tube refrigerant evaporator having tubes for conducting a freezable heat transfer fluid, a centrifugal compressor connected to withdraw and compress refrigerant vapor from the shell side of said refrigerant evaporator, an air cooled refrigerant condenser subjectable to temperatures below the freeze point of said freezable fluid and connected to receive compressed refrigerant from said compressor, and a refrigerant liquid line connected to the outlet of said air cooled condenser and the shell side of said evaporator for conducting condensed refrigerant liquid from said condenser to said evaporator; said condenser being at an elevation sufficiently above said evaporator to allow refrigerant liquid to flow through said liquid line by force of gravity from said condenser to said evaporator; a refrigerant throttling means disposed in said liquid line; a valve disposed in said liquid line for interrupting said gravitational flow of liquid refrigerant to thereby prevent freezing of the tubes of said evaporator by natural migration of the refrigerant when said air cooled condenser is of a temperature at or below the freeze point of said freezable fluid in the tubes of said evaporator; first valve control means for yieldably biasing said valve to a closed position during a period when the compressor is not operating; and second valve control means for operating said valve in response to a change in refrigerant fluid pressure within said closed refrigerant loop resulting from operation of said compressor.